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¹ Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas

In the progress made to understand the population dynamics of the Pacific sardine (Sardinops sagax) in the California Current System (CCS), two perspectives have been fundamental, the comparative approach with other ecosystems and the interdisciplinary research integrating observations, data , techniques, methods, perspectives, concepts and theories from several disciplines. Examples of integration have been studying the separate and combined effect of fishing and environmental variability; understanding the individual and superimposed effect of environmental variables of different time scales on sardine; the integration of observations and results produced by methods and techniques from different disciplines (e.g., VPA, acoustics and aerial surveys, egg and larvae surveys, egg production method); as well as data analysis with different statistical techniques and the comparison of results resulting from multiple models to achieve robust inferences. Continuing in this progressive learning to appreciate and integrate the differences that derive from different scales and theories, we present here results integrated on the basis of published knowledge related to understanding the dynamics of the sardine population, both in a holistic perspective in the CCS, as well as structured in several units. The focus is on sardine movements at different spatial scales consistent with the time scales being analyzed. The ultimate goal is to understand how sardine movements on minor spatial-temporal scales interrelate with large-scale, long-term changes in sardine abundance. To address this objective, we reconstructed the seasonal migrations and interannual spatial changes of sardine during the different stages of ENSO events over the course of the last warming period, when the bulk of the sardine biomass and the center of distribution of the population moved northward of the CCS. The analysis is based on spatially explicit monthly CPUE records of sardine caught as bait by tuna bait-boats along the southern part of the CCS over an 18-year period (1980-1997). The patterns observed in the distribution of the relative abundances of sardine in the different time scales analyzed are coherent and consistent, which allows inferring the movements of the sardine and could be used as a proxy to identify changes over time in the latitudinal distribution of environmental conditions factors that prevailed and gave rise to those patterns. For now, potential climatic drivers of spatial-temporal sardine shifts are not discussed in this presentation. The absence or inconsistency of long-term data is problematic when it comes to identifying climate drivers in the large domain of CCS. Thus, a fundamental assumption underlying the spatial-temporal changes described here is the implicit association with seasonal-scale ocean temperatures, the interannual changes in temperature associated with the different stages of ENSO events, and the regime shift toward warm ocean conditions that began in the mid-1970s.

Palabras clave: sardine; regime; Distribution

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